The physical findings, clinical signs, age, breed and sex distributions, and laboratory data of 117 dogs with untreated Cushing's syndrome were reviewed. Poodles, Dachshunds, and Boxers of all ages were found to be at increased risk, as were dogs of all breeds greater than or equal to 6 years old. Polydipsia, polyuria, progressive bilaterally symmetric alopecia, and abdominal distention were the most frequently observed clinical signs and physical findings. Lymphopenia, eosinopenia, above normal values of serum alkaline phosphatase, serum cholesterol, and sulfobromphthalein dye retention, and below normal urine specific gravity were the most frequent abnormalities found in the laboratory data. About 50% of the dogs had urinary tract infections. Final diagnosis was established on the basis of abnormally high plasma corticosteroid values in response to an intramuscular injection of adrenocorticotropic hormone.